The present invention relates to a receiver for pay television.
In a conventional pay per view system for collecting listening fees, a broadcast center (i.e., a broadcast station) mails program schedules to each user in advance. The user calls the center with predetermined data before a desired program is to be broadcast (e.g., a week or a day beforehand) so as to reserve the desired program, if any. When the desired program is on the air, the center sends an ID signal to a user who has reserved the corresponding program. When a user's receiver or decoder in the receiver receives the ID signal, a scrambled program signal is descrambled by the decoder.
The pay per view system described above has the following disadvantages:
(A) the user must call the center to reserve the desired program,
(B) each program has a reservation due date, so that the user cannot reserve the desired program when the reservation due date has passed,
(C) fees cannot be refunded even if the user does not watch the reserved program, and
(D) a spare time is required to send the ID signal to all reserved users at the beginning of every reserved program.
In another conventional pay per view system, a pay per view status signal is sent from the center to each user. When the user wishes to watch a program represented by the pay per view status signal, he depresses a pay per view switch arranged in a decoder in a tuner. The scrambled program is then descrambled, and the user can watch the program. When the user actually watches the program, charge data corresponding to the subscribed program are stored in a memory in the decoder. The center periodically checks the contents of the memory of each decoder through a telephone line and collects fees or bills the charge.
This conventional pay per view system can solve the drawbacks of the first conventional system. However, since the center must periodically check the memories of all users, the check system is complicated. Furthermore, since fee collection is performed through a telephone line, an auto dial unit and a modem (modulator/demodulator) are required, so that the user terminal and the station apparatus are complex and of high-cost.
Another pay per view system is proposed. In this system a user deposits a monetary advance to the broadcast station through a bank or the like, and the broadcast station sends the advance data together with ID (or address) data to the user via a PCM region of a TV broadcast channel. The advance data representing the deposit is stored in the advance memory of the receiver of the user. Every time the user watches a pay program, a program fee is subtracted from the advance data. According to this system, no modem for connecting the receiver to the telephone line is required. In addition, a fee collection system using a telephone line need not be installed in the broadcast center. It simplifies the system configuration.
In this pay per view system described above, since the TV broadcast channel is used as a charge link, an error may occur in advance information due to atmospheric or airplane noise. However, since the TV broadcast channel is a one-way transmission line, the transmitting center (i.e., the broadcast center) cannot detect a transmission error.